Usually, straps of wrist-watches are opened and fastened by using known fastener devices like a buckle or a clasp. The application of one of these fastener devices depends often on the material from which the watch strap is made. For example, a watch strap made from soft material like leather is fastened by actuating a buckle. By contrast, a watch strap made from rigid or metallic material is often fastened by snapping a clasp.
A watch strap having a buckle is fastened in several stages. First, an end portion of the watch strap is inserted into a first loop, then a tongue of the buckle is engaged in a strap hole and finally the buckle is fixed by inserting the end portion of the watch strap into a second loop of the buckle. The end portion is secured by sliding its end in a guide loop of the watch strap. A watch strap having a clasp, by contrast, is snapped in one or two stages by fixing the clasp to a stud of the watch strap.
Hereinafter, discussion will be limited to the advantages and disadvantages of a clasp fastener of a watch strap.
A clasp fastener is generally provided with an adjusted closing force. Usually, the closing force is regulated during manufacture and is adjustable by a specialist during maintenance of the watch strap. This force can differ in function of the watch strap model chosen. Models destined for male or sporting users are activated with a closing force higher than that of a model destined for female users. One disadvantage is that the closing force of a watch strap clasp cannot be regulated by users as a function of daily or leisure activities.
A clasp fastener which is not provided with a security device for securing its fastening procedure, can, in accordance with the strength of the closing force, open as the result of a heavy shock, for example during a sport activity. One disadvantage is that a watch strap clasp having no security device cannot prevent unintentional fastener opening.